A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• either onto the C=C or C=O bond. The present work should also be considered as an extension of our earlier studies focused on the exploration of 1,4-quinones in the [3 + 2]-cycloaddition and hetero-Diels–Alder reaction performed with thiocarbonyl S-methanides and thiochalcones, respectively [37][38

Ferrocenyl-substituted tetrahydrothiophenes via formal [3 + 2]-cycloaddition reactions of ferrocenyl thioketones with donor–acceptor cyclopropanes

• Grzegorz Mlostoń,
• Mateusz Kowalczyk,
• André U. Augustin,
• Peter G. Jones and
• Daniel B. Werz

Beilstein J. Org. Chem. 2020, 16, 1288–1295, doi:10.3762/bjoc.16.109

• of the zwitterionic intermediate 10 led to the formation of the tetrahydrothiophene derivative 9. This process formally resembled the [3 + 2]-cycloadditions of thiocarbonyl S-methanides with an activated C–C double bond, which also led to tetrahydrothiophenes [6][7][8]. Nevertheless, the key step

• practical importance [1][2]. The development of chemo- and diastereoselective syntheses for these compounds is thus a challenging problem. An elegant and highly efficient method for the construction of the tetrahydrothiophene ring is based on 1,3-dipolar cycloadditions of in-situ-generated thiocarbonyl S

• -methanides (thiocarbonyl ylides) with electron-deficient ethylenic dipolarophiles. This method was extensively developed by Huisgen and co-workers in the 1980s [3][4][5]. In the course of these studies, a non-orthodox stepwise mechanism of the 1,3-dipolar cycloaddition was established by experiments

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• isomeric homo-Diels–Alder adducts were found in the mixture. [3 + 2]-Cycloadditions (1,3-dipolar cycloadditions) Electron-rich 1,3-dipoles such as thiocarbonyl S-methanides and azomethine ylides react with dipolarophiles E-1 and Z-1 to give five-membered cycloadducts through stepwise zwitterionic reaction

• with thiolanes 19b. Their formation proves the appearance of the labile seven-membered ketenimine 31b, which exists in equilibrium with zwitterion 18b. Ketenimine 31b is efficiently trapped with water to give 30b. Analogous results were obtained with different thiocarbonyl S-methanides 16, generated

• from the corresponding precursors 17 with methyl, ethyl and isopropyl esters of type E- and Z-1 [19][33][34][35][36]. Remarkably, the reactions of (E)- and (Z)-1b with thiocarbonyl S-methanides 16b-e, in contrast to the corresponding S-isopropanide 16a (Scheme 5), occurred without formation of

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• intermediate, delocalized diradical species. The influence of selenium as a ‘heavy atom’ for stabilization of this intermediate has been emphasized. Keywords: 1,3-dipolar cycloadditions; reaction mechanisms; reactive intermediates; thiocarbonyl S-methanides; thioketones; Introduction Thiocarbonyl S

• decomposition, 2,2-diaryl-substituted derivatives can be generated only at low temperature, typically at −60 °C in THF solution. The in situ generated thiocarbonyl S-methanides 1 are considered as electron-rich 1,3-dipoles, which easily react with electron-deficient dipolarophiles, yielding a plethora of five

• -membered heterocycles [2]. In addition, some cycloaliphatic thiocarbonyl S-methanides were shown to react with strongly electron-deficient cyano-substituted ethenes via zwitterionic intermediates to yield also seven-membered cyclic ketene imines, which easily undergo further conversions [3][4][5]. In the

Synthesis of ferrocenyl-substituted 1,3-dithiolanes via [3 + 2]-cycloadditions of ferrocenyl hetaryl thioketones with thiocarbonyl S-methanides

• Grzegorz Mlostoń,
• Róża Hamera-Fałdyga,
• Anthony Linden and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2016, 12, 1421–1427, doi:10.3762/bjoc.12.136

• Ferrocenyl hetaryl thioketones react smoothly with in situ generated thiocarbonyl S-methanides to give 1,3-dithiolanes. In the case of aromatic S-methanides, the sterically more crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes (2-CH2 isomers) were formed as sole products. The reactions with cycloaliphatic S

• ; ferrocene; thiocarbonyl S-methanides; thioketones; Introduction In a recent publication, a straightforward method for the synthesis of hitherto little known ferrocenyl aryl/hetaryl thioketones of type 1 via a standard procedure by treatment of the corresponding ferrocenyl ketones with Lawesson reagent was

• ‘superdienophiles’ [3]. The reactive thiocarbonyl S-methanides of type 2 can conveniently be generated by thermal elimination of N2 from 1,3,4-thiadiazoles 3 at ca. −45 °C in the case of 2,2-diaryl derivatives 3a,b or upon gentle heating of cycloaliphatic precursors 3c,d in THF solution to ca. +45 °C [4][5]. The [3

Diradical reaction mechanisms in [3 + 2]-cycloadditions of hetaryl thioketones with alkyl- or trimethylsilyl-substituted diazomethanes

• Grzegorz Mlostoń,
• Paulina Pipiak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2016, 12, 716–724, doi:10.3762/bjoc.12.71

• diradical mechanism postulated for the formal [3 + 2]-cycloaddition of aryl/hetaryl thioketones 1 with the in situ generated thiocarbonyl S-methanides [28]. The missing formation of dimers from thiocarbonyl ylides 3 derived from hetaryl thioketones can be explained by steric hindrance resulting from the